1. Field of the Invention
The invention relates generally to a power steering system; and, more specifically, to an apparatus for detecting friction in a steering gear of such a power steering system.
2. Description of Related Art
Rack-and-pinion power steering systems may utilize a steering gear having a ball screw. In addition, such systems may also use electric power assistance and are typically referred to as Rack Electric Power Assisted Steering (REPAS). Due to moisture and dirt entering the steering system, in particular the steering gear, rust may form in or on the components of the steering system. In particular on the ball raceways of the steering rack, on the balls of the recirculating ball gear and on the raceways of the recirculating ball gear, all of which increases the friction of the steering system. However, since a failure of the electrical assistance is to be expected only when the formation of rust has progressed a long way and the frictional forces have increased greatly, there is no initial adverse effect for the driver. That is since the electrical assistance compensates for the friction it may not be apparent until the assistance unit fails to overcome the frictional forces. For this reason, prompt warning of the driver is therefore desirable.
Methods for detecting friction in a steering system are known; however, these methods are not capable of determining the friction within the steering gear separately from other influences such as the friction of the components connected to the steering gear; for example, the pivot bearings and shock absorbers. Therefore, such solutions require replacement of the entire steering system due to a finding of increased friction, even though the steering system itself does not exhibit any formation of rust or increased friction, that is the steering system or steering gear is undamaged. Accordingly, such methods are systems for detecting friction may lead to still functionally capable steering gears being undesirably replaced.
The object of the invention is therefore to introduce a system that detects increased friction in a steering gear of a steering system.